1. Field of the Invention
This invention relates to a process for depolymerizing oligomers of p-(.alpha.-methylene-alkyl)phenols and is more particularly concerned with a process for converting said oligomers and the corresponding monomers to hydroquinone and related compounds.
2. Description of the Prior Art
Attention has recently been focused on the preparation of p-isopropenylphenol and the utilization of this compound in a variety of ways. For example, U.S. Pat. No. 4,207,265 describes the oxidation of p-isopropenylphenol to hydroquinone in high yield and also discloses a semi-continuous process in which phenol and acetone are condensed to form Bisphenol A, the latter is subjected to alkaline cleavage to give a mixture of phenol and p-isopropenylphenol, which latter is oxidized to hydroquinone and acetone and the recovered phenol and acetone are re-used in the synthesis of further Bisphenol A.
U.S. Pat. No. 4,054,611 describes a method of preparing p-isopropenylphenol in high yield in the form of a stable solution by condensing the vapor of p-isopropenylphenol in a solvent such as an alcohol as it is formed by thermal decomposition of Bisphenol A. This same reference refers to the problem of handling p-isopropenylphenol in solid, isolated form because of its tendency to polymerize to form a mixture of oligomers even at room temperature. It is shown that any oligomers so formed can be decomposed by heating at temperatures of 150.degree. C. to 260.degree. C. and collecting the monomer so produced by passing the vapors into a solvent such as alcohol.
German Application No. 2,508,512 describes the cracking of oligomers of p-isopropenylphenol by heating at 60.degree. to 300.degree. C. over an acid clay catalyst.
We have now found that it is possible to recover useful products, i.e. hydroquinone and derivatives thereof, from the oligomers of p-isopropenylphenol and related p-(.alpha.-methylenealkyl)phenols, as well as the alkyl ethers and acylated derivatives thereof, by a relatively simple procedure which does not involve the use of elevated temperatures or any form of thermal cracking.